As an example of the above-mentioned pump unit, a micro pump assembly disclosed in Patent Document 1 is known.
The assembly includes a pump having a piezoelectric element and a discharge mechanism for discharging fluid according to operation of the piezoelectric element, a basal plate to which the pump is attached, and a gasket disposed between the pump and the basal plate.
The discharge mechanism includes a pump body, a pump side diaphragm defining a pump chamber in cooperation with the pump body, a flow-in valve that is disposed in a flow-in passage defined in the pump body and connecting with the pump chamber, and a flow-out valve that is disposed in a flow-out passage defined in the pump body and connecting with the pump chamber.
The pump-side diaphragm vibrates according to operation of the piezoelectric element to thereby repeatedly increase and reduce the volume of the pump chamber.
The flow-in valve opens when the pressure on the upstream side of the flow-in valve is greater than the pressure in the pump chamber. The flow-out valve opens when the pressure in the pump chamber is greater than the pressure on the downstream side of the flow-out valve.
Therefore, when the volume in the pump chamber increases owing to vibration of the pump-side diaphragm, the flow-in valve opens and the flow-out valve closes to suck fluid into the pump chamber through the flow-in passage. On the other hand, when the volume in the pump chamber decreases owing to vibration of the pump side diaphragm, the flow-in valve closes and the flow-out valve opens to cause fluid to flow out of the pump chamber through the flow-out passage.
As mentioned above, the flow-in valve and the flow-out valve open when the pressure on its upstream side is greater than the pressure on its downstream side, and therefore, when the pressure on the upstream side of the pump increases, fluid may undesirably be caused to flow out through the flow-out passage.
Accordingly, the basal plate includes a valve mechanism for restricting flow of fluid when the pressure in the flow-in passage increases.
Specifically, the valve mechanism includes a valve mechanism body having a flow-in side connection passage connecting with the flow-in passage, and a flow-out side connection passage connecting with the flow-out passage, and a valve side diaphragm disposed in the valve mechanism body and dividing the flow-in side connection passage from the flow-out side passage.
When the pressure in the flow-in side connection passage is greater than the pressure in the flow-out side connection passage, the pressure difference causes the valve side diaphragm to be pushed in a direction to close the flow-out side connection passage. Consequently, flow of fluid through the flow-out side passage is restricted when the pressure on the upstream side of the pump increases.
However, in the pump unit disclosed in Patent Document 1, the pump is attached to the valve mechanism (basal plate) via the gasket. The gasket is provided to seal the junction between the pump and the valve mechanism, and is formed by supplying uncured elastomer by screen printing and subsequently heating the uncured elastomer to cure it.
Thus, the provision of the gasket in the pump unit of Patent Document 1 results in increase in the number of components, and requires a step for forming the gasket in the joint between the pump and the valve mechanism, which makes a manufacturing process complicated.